The present invention relates to a method and apparatus for managing digital watermark information to be embedded into digital data of an image or audio, and a storage medium which stores a program for executing the method.
Recent development of computers and networks is remarkable, and various kinds of information such as text data, image data, and audio data are processed in a computer or network. Since such data is digital data, copy data with the same quality can be easily obtained. To protect the copyright for such data, copyright information or user information is often embedded into image data or audio data as a digital watermark. The digital watermark is a technique of executing predetermined processing for image data or audio data to secretly embed another information into the data.
When watermark information is extracted from data having a digital watermark embedded therein, the copyright information, user information, and identification information of the data can be obtained. In addition, an illicit copy can be traced using such an digital watermark.
As the first condition required for such a digital watermark, a watermark is embedded such that the embedded information is imperceptible, i.e., degradation in quality of original digital information is suppressed (quality). As the second condition, the watermark information embedded in digital information continues to remain, i.e., the embedded watermark information is not lost even by editing processing such as data compression or filtering or an attack such as alteration (resiliency). As the third condition, the amount of watermark information to be embedded can be selected in accordance with the application purpose (information amount). These conditions required for a digital watermark generally have tradeoff relationships. For example, when a highly resilient digital watermark is realized, degradation in quality becomes relatively large, or the embeddable watermark information amount becomes small in many cases.
For, e.g., a multilevel still image, the digital watermark embedding methods can be roughly classified into a scheme of embedding a watermark in the space domain and a scheme of embedding a watermark in the frequency domain. Various methods to be described below are known.
As the former scheme of embedding a digital watermark in the space domain by patchwork, an IBM scheme (W. Bender, D. Gruhl, and N. Morimoto, Techniques for Data Hiding, xe2x80x9cProceedings of the SPIExe2x80x9d, San Jose Calif., USA, February 1995) and G. B. Rhoads and W. Linn; xe2x80x9cSteganographymethods employing embeddedxe2x80x9d, U.S. Pat. No. 5,636,292 are present.
Examples of the latter scheme of embedding a digital watermark in the frequency domain are an NTT scheme using the discrete cosine transform (Nakamura, Ogawa, and Takashima xe2x80x9cDigital Watermarking Scheme in Frequency Domain for Copyright Protection of Digital Imagexe2x80x9d, SCIS""97-26A, January 1997), a Defense Academy scheme using the discrete Fourier transform (Onishi, Oka, and Matsui, xe2x80x9cWatermark Signature Method for Image Using PN Sequencexe2x80x9d, SCIS""97-26B, January 1997), a Mitsubishi/Kyushu University scheme using the discrete wavelet transform (Ishizuka, Sakai, and Sakurai, xe2x80x9cExperimental Examination About Security and Reliability of Digital Watermark Technique Using Wavelet Transformxe2x80x9d, SCIS""97-26D, January 1997), and a Matsushita scheme (Inoue, Miyazaki, Yamamoto, and Katsura, xe2x80x9cRobustness of Digital Watermark Image Compression and Transformation Based on Wavelet Transformxe2x80x9d, SCIS""98-3.2.A, January 1998) In the above schemes, digital watermark embedding processing and extraction processing are in a one-to-one correspondence. The schemes are not compatible with each other. As is generally said, the technique of embedding a digital watermark in the space domain suffers little degradation in quality but is poor in resiliency, while the scheme using frequency transform suffers large degradation in quality but is excellent in resiliency. These schemes have different characteristic features, so some techniques are excellent in resiliency but can embed only a small amount of watermark information, and some techniques suffer little degradation in quality but are poor in resiliency. In addition, to protect information having a watermark, the algorithm for embedding the digital watermark, and information representing the embedding position or change amount (to be referred to as a key hereinafter) are often kept secret. This aims at increasing the resiliency against an intentional attack of trying to remove the digital watermark by analyzing the algorithm or embedding position.
A digital watermark is generally imperceptible to the human, though it is sometimes called an invisible digital watermark. In this case, a digital watermark that visibly synthetically displays a maker logo or the like on an original image is sometimes called a visible digital watermark.
As described above, there are various digital watermarking schemes.
Conventionally, no technique of managing the digital watermark information embedding scheme for image data on the basis of time information has been established. Hence, the digital watermarking scheme cannot be always optimized on the basis of the use period/use form of the image data.
In use of different digital watermarking schemes, even when watermark information embedded in an image is to be extracted, it cannot be done unless the scheme and version of digital watermark embedding are known in advance.
If an embedded watermark cannot be extracted, it cannot be determined whether the watermark is embedded by another scheme, or the embedded watermark is destroyed by an attack.
The present invention has been made in consideration of the above prior art, and has as its main object to provide a technique capable of always keeping digital watermark information embedded in image data by an optimum scheme on the basis of a time factor, or removing a digital watermark, or erasing the image data.
It is another object of the present invention to provide a data processing method and apparatus capable of efficiently coping with various digital watermarks and extracting the digital watermarks.
It is still another object of the present invention to provide a data processing method and apparatus capable of detecting various watermarks and also detecting whether the watermarks are destroyed by an attack or the like.
In order to attain the above described objects, a data processing apparatus of the present invention, comprises: holding means for holding image data having additional information embedded as a digital watermark; detection means for detecting time information related to the image data; and change means for changing an embedding scheme for the additional information as the digital watermark embedded in the image data on the basis of the detected time information.
In a data processing apparatus of the present invention, the data processing apparatus for embedding a digital watermark into digital data, comprises: watermark embedding means for embedding watermark information to be embedded into the digital data; and common watermark embedding means for embedding, into the digital data, version information for specifying a version of an embedding scheme used by the watermark embedding means.
Further, in a data processing apparatus of the present invention, the data processing apparatus for extracting the watermark information from the digital data in which the watermark information is embedded by the above described data processing apparatus, comprises: common watermark extraction means for extracting the version information embedded by said common watermark embedding means; specifying means for specifying, on the basis of the version information extracted by the common watermark extraction means, the version of the embedding scheme with which the watermark information is embedded into the digital data; selection means for selecting watermark extraction means capable of extracting watermark information corresponding to the version specified by the specifying means; and control means for controlling to extract the watermark information from the digital data using the watermark extraction means selected by the selection means.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.